Lightweight cooling fabric and articles made therefrom

ABSTRACT

A lightweight knit fabric, has a knit structure prepared from at least 80 wt % of one or more yarns having a hydrophobic surface containing less than 1 part hydroxyl group per 10 million parts of (co)polymer forming the one or more yarns, and articles prepared therefrom, which provide efficient moisture transport and cooling effects on a subject in contact therewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lightweight fabric that provides cooling effects to the wearer, and to articles made therefrom.

2. Description of the Related Art

Heat exhaustion is a problem that affects human beings in a variety of occupations and environments around the world. According to Joseph Rampulla, MS, APRN, BC “Heat illness is generally underreported, and the true incidence is unknown. Death rates from other causes (e.g. cardiovascular, respiratory) increase during heat waves but are generally not reflected in the morbidity and mortality statistics related to heat illness. Nonetheless, heat waves account for more deaths than all other natural disasters combined in the USA.” From police and paramedics to construction workers and laborers, or service men and women engaging in strenuous exercise and physical training, hot and humid conditions degrade performance abilities and lead to injuries, fainting, and other more serious medical conditions.

Most of the available products today use lightweight polyester material with a finish that wicks moisture to create a lightweight fabric that will wick moisture away from the body. This creates a material that has some properties that will keep you cool (wicking pulls sweat away from your skin). While polyester is a durable fiber, it does best to insulate your body in cold temperatures. Fabrics and shirts made from polyester, with a wicking finish are readily available from every major sportswear company. The effectiveness of these polyester wicking fabrics at keeping your body comfortable in heat and humidity is minimal and quickly dissipates as the fiber becomes overloaded with body heat and perspiration.

Accordingly, a lightweight fabric is needed that will provide high levels of wicking, and result in highly efficient cooling of the wearer.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a lightweight fabric that provides a wicking effect to more efficiently transport moisture, preferably coupled with an extremely high rate of evaporation, which provides a cooling effect on a subject in contact with the fabric.

A further object of the present invention is to provide an article formed from the present invention fabric, which keeps the wearer dry and cool even during strenuous activity.

Another object of the present invention is to provide an article formed from the present invention fabric, which can be used in bed linens or bandages, particularly for treatment of burn victims, which will not adhere to burned tissue, and provides a cooling effect on the subject in contact therewith.

These and other objects of the present invention, alone or in combinations thereof, have been satisfied by the discovery of a lightweight knit fabric, comprising a knit structure prepared from at least 80 wt % of one or more yarns having a hydrophobic surface containing less than 1 part hydroxyl group per 10 million parts of (co)polymer forming the yarn, and articles prepared therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 shows a graph of drying times comparing a shirt in accordance with the present invention compared to three commercially available alternative shirts, and showing significant improvements in drying time for the present invention shirt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “fiber” as used herein refers to a fundamental component used in the assembly of yarns and fabrics. Generally, a fiber is a component which has a length dimension which is much greater than its diameter or width. This term includes ribbon, strip, staple, and other forms of chopped, cut or discontinuous fiber and the like having a regular or irregular cross section. “Fiber” also includes a plurality of any one of the above or a combination of the above.

As used herein, the term “high performance fiber” means that class of synthetic or natural non-glass fibers having high values of tenacity greater than 10 g/denier, such that they lend themselves for applications where high abrasion and/or cut resistance is important. Typically, high performance fibers have a very high degree of molecular orientation and crystallinity in the final fiber structure.

The term “filament” as used herein refers to a fiber of indefinite or extreme length such as found naturally in silk. This term also refers to manufactured fibers produced by, among other things, extrusion processes. Individual filaments making up a fiber may have any one of a variety of cross sections to include round, serrated or crenular, bean-shaped or others.

The term “yarn” as used herein refers to a continuous strand of textile fibers, filaments or material in a form suitable for knitting, weaving, or otherwise intertwining to form a textile fabric. Yarn can occur in a variety of forms to include a spun yarn consisting of staple fibers usually bound together by twist; a multi filament yarn consisting of many continuous filaments or strands; or a mono filament yarn which consists of a single strand. A “blended yarn” as used herein refers to a yarn that comprises an intimate blend of at least two different types of fibers.

The term “composite yarn” refers to a yarn prepared from two or more yarns, which can be the same or different. Composite yarn can occur in a variety of forms wherein the two or more yarns are in differing orientations relative to one another. The two or more yarns can, for example, be parallel, wrapped one around the other(s), twisted together, or combinations of any or all of these, as well as other orientations, depending on the properties of the composite yarn desired. Examples of such composite yarns are provided in U.S. Pat. No. 4,777,789, U.S. Pat. No. 4,838,017, U.S. Pat. No. 4,936,085, U.S. Pat. No. 5,177,948, U.S. Pat. No. 5,628,172, U.S. Pat. No. 5,632,137, U.S. Pat. No. 5,644,907, U.S. Pat. No. 5,655,358, U.S. Pat. No. 5,845,476, U.S. Pat. No. 6,212,914, U.S. Pat. No. 6,230,524, U.S. Pat. No. 6,341,483, U.S. Pat. No. 6,349,531, U.S. Pat. No. 6,363,703, U.S. Pat. No. 6,367,290, and U.S. Pat. No. 6,381,940 (collectively, the “Kolmes patents”), the contents of each of which are hereby incorporated by reference.

For convenience, the term “yarn component” as used herein, encompasses fiber, monofilament, multifilament and yarn.

The present invention relates to a lightweight fabric comprising a knit structure prepared from at least 80 wt % of one or more yarns having a hydrophobic surface containing less than 1 part hydroxyl groups on the surface of the yarn per 10 million parts of (co)polymer forming the one or more yarns. Preferably, the fabric has a fabric weight of less than 10 ounces per square yard (OPSY), more preferably less than 6 OPSY, most preferably less than 5 OPSY. The knit fabric is preferably formed from at least 85 wt % of the one or more yarns having the hydrophobic surface, more preferably at least 90 wt % of the one or more yarns having the hydrophobic surface, most preferably 95-100 wt % of the one or more yarns having the hydrophobic surface. Ideally, and in a most preferred embodiment, the one or more yarns having the hydrophobic surface is a linear low density polyethylene (LLDPE) yarn, which can optionally contain one or more comonomers such as other alpha olefins.

The lightweight knit fabric of the present invention preferably has the one or more yarns being a yarn prepared from at least 70 wt % linear low density polyolefin. More preferably, the yarn is linear low density polyethylene, optionally containing up to 30 wt % of one or more α-olefin comonomers. The one or more α-olefin comonomers are preferably at least one member selected from the group consisting of propylene, n-butene, n-hexane, and n-octene. When present, the one or more α-olefin comonomers is preferably present in an amount of 10 to 30 wt %, based on total yarn weight.

In the present invention, the linear low density polyolefin preferably has a weight average molecular weight of 10,000 or more.

In a most preferred embodiment, the one or more yarns making up the present invention fabric have no surface hydroxyl groups.

The lightweight knit fabric of the present invention is preferably made using a linear stitch or a jersey stitch.

In order to provide form fitting properties to the lightweight fabric of the present invention, the fabric can optionally comprise up to 4 wt %, preferably 2-4 wt %, more preferably 3 wt %, of an elastomeric yarn, so long as the elastomeric yarn does not interfere with the moisture transport and cooling properties of the fabric.

Several factors are important when trying to design a cooling and wicking fabric according to the present invention:

It is important for the fabric to be form fitting in order to keep the skin as dry as possible to keep the skin cool;

It is important not to let water bond to the material, by maintaining a hydrophobic surface of the yarn used in making the garment or article (shirt, headband, etc.,); and

It is important not to let the material absorb sweat.

If sweat pools on the skin, it then blocks the transport of the sweat to the outside of the shirt and the body will still be hot and uncomfortable even if the shirt is cool on the outside. Moisture must be evaporated from the skin rather than from the shirt to keep the skin cool.

The present invention yarn is made from a (co)polymer designed by its constituents to be hydrophobic. The filaments in the fiber bundle are designed to maximize the volume of the copolymer while minimizing the surface area of the filament consistent with good hand (comfort) on the fabric while achieving the smallest amount of surface area possible in the fiber bundle. There should be space in the fabric to allow the sweat to travel to the surface of the apparel. The copolymer is formulated to have almost no hydroxyl groups on the surface of the copolymer that would bond with the water molecules contained in perspiration. The bonded water is harder to remove from the copolymer and that is typically what keeps fabrics wet, thus keeping the skin wet and decreasing the evaporation rate. It is academic that “bound water” takes extra energy to transport and evaporate, therefore, eliminating the hydroxyl groups from the copolymer allows for faster transportation and evaporation of sweat away from the body. This prevents the “water logging” effect and allows the cooling to be continuous. Thus, some conventional cooling shirts are able to cool for a short time until the “water logging” effect takes over which effectively stops the cooling. The present invention fabric, on the other hand, provides both a rapid transport of water from the skin, and a rapid drying of the water from the surface of the fabric in order to maintain the drying and cooling properties over the course of wearing or using the article made from the fabric.

The present invention fabric is also perfect for bandages, sheets, and pillowcases, and for burn victim treatment because the fiber will not absorb fluids and wicks moisture away from wounds. Further, particularly for burn victims, the fabric of the present invention does not adhere to wounds, thus adding to comfort, and providing a cooling feeling to the site of the burn. Thus, the present invention fabric has unlimited applications in the areas of apparel, bedding, and health and safety.

In the present invention, the fabric can be formed into articles, preferably into an article selected from the group consisting of garments, bed sheets, pillowcases, and bandages. When the article is a garment, it is preferably a member selected from the group consisting of shirts, undergarments, socks, leggings, biking pants/shorts and tights. When the garment is a shirt, it can be either short-sleeved or long-sleeved, and when the garment is biking pants it can be either long legged or shorts.

The present invention fabric is prepared primarily from fibers having less than 1 part hydroxyl groups in the copolymer per 10 million parts of copolymer/fiber, particularly on the fiber surface. Preferably, the fiber has no hydroxyl groups in the copolymer, unlike cotton, polyester, nylon and wool. Therefore, the present invention fabric has excellent moisture transport and evaporation, which is superior to other available fabrics. The skin is kept drier and therefore is cooler.

Linear low-density polyethylene (LLDPE) is typically a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. These other comonomers can be present in amounts up to 30 wt % of the polymer, preferably from 10-30 wt % of the polymer. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties. LLDPE yarn is commercially available from a variety of manufacturers, such as Fiber Science, Inc. The LLDPE yarn for use in the present invention is typically a multifilament yarn, having a total denier of 70 to 300, preferably 150 to 200.

If desired, in order to modify the physical properties of the fabric of the present invention, it is possible to include up to 20 wt % of one or more other types of yarn, so long as the one or more other yarns do not contain hydrophilic surfaces sufficient to detract from the wicking and cooling properties of the present invention. Most preferably, no other type of yarn is used in the fabric of the present invention, with the exception of thread used to stitch parts of the fabric together at the seams. In a particularly preferred embodiment, a garment formed from the present invention fabric is formed by shaped knitting (knitting that uses dropped stitches in order to generate a garment in a particular shape, with minimal seams in construction).

If the one or more additional yarns are included, the yarn can be any of a variety of types of yarn. One type of yarn that may be present is an elastomeric yarn if desired. As the elastomeric yarn component, any elastomeric fiber may be used, as monofilament or multifilament yarn. However, due to the hydrophilicity of the surface of typical elastomeric yarns, their use should be kept at a minimum if at all possible. An elastomer is a natural or synthetic polymer that, at room temperature, can be stretched and expanded to typically twice its original length. After removal of the tensile load it will immediately return to its original length. Along with spandex, rubber and anidex (no longer produced in the United States) are considered elastomeric fibers. Spun from a block copolymer, spandex fibers exploit the high crystallinity and hardness of polyurethane segments, yet remain “rubbery” due to alternating segments of polyethylene glycol. Suitable elastomeric fibers include, but are not limited to, fibers made from copolymers having both rigid and flexible segments in the polymer chains, such as, for example, block copolymers of polyurethane and polyethylene glycol. Particularly suitable elastomeric fibers include, but are not limited to, Spandex, such as LYCRA (produced by United Yarn Products), ELASPAN (produced by Invista), DORLASTAN (produced by Bayer), CLEAR SPAN (produced by Radici) and LINEL (produced by Fillattice).

Elastomeric yarns can have one or more of the following materials properties: can be stretched over 500% without breaking; able to be stretched repetitively and still recover original length; lightweight; abrasion resistant; poor strength, but stronger and more durable than rubber; soft, smooth, and supple; resistant to body oils, perspiration, lotions, and detergents; no static or pilling problem; very comfortable; and easily dyed.

The elastomeric yarn can be any desired denier, preferably from 10 to 210, more preferably from 15 to 150, most preferably from 20 to 75. The elastomeric yarn can be used alone or combined with one or more other yarns of any desired type, so long as the combination retains its elastomeric properties. If combined with one or more other yarns, the elastomeric yarn and other yarns are preferably blended, or the one or more other yarns are wrapped around the elastomeric yarn to provide an elastomeric core composite yarn, thus retaining the stretch property.

Elastomeric yarn containing composite yarns are further described in U.S. Pat. Nos. 5,568,657 and 5,442,815, the contents of which are incorporated herein by reference. Elastomeric yarn containing composite yarns having wicking properties are described in U.S. Provisional Application Serial No. 61/020,790, filed Jan. 14, 2008, the contents of which are hereby incorporated by reference.

If high strength, tenacity and/or cut resistance are desired, it is also possible to include small amounts of a high performance fiber in the present invention fabric. The high performance fiber can be any desired high performance fiber. However, from the point of view of maintaining the hydrophobic surface of the yarn in the fabric, the high performance fiber preferably comprises a high molecular weight polyolefin, preferably high molecular weight polyethylene or high molecular weight polypropylene.

U.S. Pat. No. 4,457,985, hereby incorporated by reference, generally discusses high molecular weight polyethylene and polypropylene fibers. In the case of polyethylene, suitable fibers are those of molecular weight of at least 150,000, preferably at least 400,000, more preferably at least one million and most preferably between two million and five million. Such extended chain polyethylene (ECPE) fibers may be grown in solution as described in U.S. Pat. No. 4,137,394 or U.S. Pat. No. 4,356,138, hereby incorporated by reference, or may be a filament spun from a solution to form a gel structure, as described in German Off. 3 004 699 and GB 2 051 667, and especially described in U.S. Pat. No. 4,551,296, hereby incorporated by reference. As used herein, the term polyethylene preferably means a predominantly linear polyethylene material that may contain minor amounts of chain branching or comonomers not exceeding 5 modifying units per 100 main chain carbon atoms, and that may also contain admixed therewith not more than about 50 weight percent of one or more polymeric additives such as alkene-1-polymers, in particular low density polyethylene, polypropylene or polybutylene, or copolymers containing mono-olefins as primary monomers. Depending upon the formation technique, the draw ratio and temperatures, and other conditions, a variety of properties can be imparted to these fibers. The tenacity of the fibers should preferably be at least 15 g/d, more preferably at least 20 g/d, even more preferably at least 25 g/d and most preferably at least 28 g/d. Similarly, the tensile modulus of the filaments, as measured by an Instron tensile testing machine, is preferably at least 300 g/d, more preferably at least 500 g/d and still more preferably at least 1,000 g/d and most preferably at least 1,200 g/d. These highest values for tensile modulus and tenacity are generally obtainable only by employing solution grown or gel fiber processes. For example, high molecular weight polyethylene filaments produced commercially by Honeywell Corp. under the trade name SPECTRA or by DSM under the trade name DYNEEMA and having moderately high moduli and tenacity are particularly useful.

Similarly, highly oriented polypropylene of molecular weight at least 200,000, preferably at least one million and more preferably at least two million, may be used. Such high molecular weight polypropylene may be formed into reasonably well oriented fibers by techniques described in the various references referred to above, and especially by the technique of U.S. Pat. Nos. 4,663,101 and 4,784,820, hereby incorporated by reference, and U.S. patent application Ser. No. 069,684, filed Jul. 6, 1987 (see published application WO 89 00213). Since polypropylene is a much less crystalline material than polyethylene and contains pendant methyl groups, tenacity values achievable with polypropylene are generally substantially lower than the corresponding values for polyethylene. Accordingly, a suitable tenacity is at least about 8 g/d, with a preferred tenacity being at least about 11 g/d. The tensile modulus for polypropylene is at least about 160 g/d, preferably at least about 200 g/d.

The high performance yarn can be any desired denier, preferably from 10 to 325, more preferably from 50 to 250, most preferably from 100 to 220.

The present invention fabric and articles produced therefrom provide a noticeable and remarkable cooling effect on a person touching or wearing the articles. The present invention fabric has been found to dry nearly four times faster than typical commercially available “cool t-shirts” in laboratory tests. The present invention fabric is made from a fiber that transmits water from the skin to the outer surface of the t-shirt in an extremely efficient way that is far superior to cotton or polyester because the wicking ability is due to the structure, and particularly the surface properties, of the fiber from which the fabric/article is made. This wicking coupled with rapid evaporation on the surface of the fabric translates into remarkably cool t-shirts and apparel that keep personnel comfortable during work and exercise or when used as bandages, or bedding as sheets and pillowcases. The performance advantage over typical so-called polyester “cooling t-shirts” is twofold: the present invention fabric achieves superior cooling by transporting and evaporating moisture at an exceptionally high rate, and the present invention fabric technology does not trap and hold heat like polyester. In fact, the present invention yarn is up to 45% lighter than polyester.

An embodiment of the present invention fabric (having a fabric weight of 6 OPSY, prepared from 100% LLDPE yarn) was prepared and tested for drying time against three commercially available products, a 100% cotton shirt, a shirt sold by DeFeet® under the brand name UND-ICE EXTREME, a shirt sold by UnderArmour® under the brand name COLD BLACK, and made predominantly from polyester. The drying conditions were at a room temperature of 69.8° F., and a relative humidity of 15.5%. In the graph shown in FIG. 1, the present invention t-shirt dried approximately four times faster than the UnderArmor shirt. The only product even close to the present invention is the DeFeet® shirt, which is a predecessor product made by the present applicant for DeFeet®. None of the comparative shirts tested contain the LLDPE based fabric of the present invention. One factor that is important to obtaining the present invention cooling effect (in a garment) is that the garment fits properly. Although this seems elementary, it is noteworthy that improperly fitting t-shirts will pool the sweat on the skin and thereby prevent cooling. Accordingly, garments made from the present invention fabric are preferably designed to be thin, and therefore minimize the insulation (of the fabric) from interfering with the cooling feeling from the evaporation of the sweat, and are designed to be substantially form fitting, in order to maintain at least a minimum level of contact with the skin of the wearer, in order to enable the wicking properties of the fabric to act most efficiently. This fabric can be made into under garments, helmet liners, sleeves, socks, bedding and other apparel items.

The present invention fabric was also tested for cooling ability. A preferred embodiment of the present invention fabric was prepared into a biking shirt (having fabric weight of 6 OPSY, and formed from 100% LLDPE, except for the thread stitching seams together). The shirt was compared to a commercially available biking shirt having a similar fabric weight as the present invention shirt. The shirts were each individually worn by a bicyclist on a stationary bike in an ambient temperature controlled environment, with temperature measurements taking at mid-chest level using thermal imaging. With the help of a power/wattage meter hooked to the stationary bike, the subject was pedaling at an equal effort for four separate sessions and the images were shot after 5 minutes of exercise, wearing each shirt, with and without a fan blowing on the biker. The commercially available product product was shot after 5 minutes of work with no air movement and 5 minutes of work with a fan blowing at 5 mph directly at the subject. The same scenario was done for the present invention product. The comparative shirt at 5 minutes with no fan gave a temperature reading of 82.6° F., while the present invention product at 5 minutes with no fan gave a temperature reading of 79.8° F. The comparative shirt at 5 minutes with fan gave a temperature reading of 79.7° F., while the present invention product at 5 minutes with fan gave a temperature reading of 70.9° F. This corresponds to a temperature reduction with fan using the present invention product of 11%, compared to a reduction of only 3.5% for the comparative shirt! The present invention fabric provided significantly improved cooling, with or without fan, with the subject being kept between 2.8 and 8.9 degrees cooler than the commercially available comparative shirt.

The present invention fabric provides significantly more efficient moisture transport and evaporation, keeping the skin drier and therefore keeping the subject cooler.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. A lightweight knit fabric, comprising a knit structure prepared from at least 80 wt % of one or more yarns having a hydrophobic surface containing less than 1 part hydroxyl groups per 10 million parts of (co)polymer forming the one or more yarns.
 2. The lightweight knit fabric of claim 1, wherein the one or more yarns is a yarn prepared from at least 70 wt % linear low density polyolefin.
 3. The lightweight knit fabric of claim 2, wherein the yarn is linear low density polyethylene, optionally containing up to 30 wt % of one or more α-olefin comonomers.
 4. The lightweight knit fabric of claim 3, wherein the one or more α-olefin comonomers is at least one member selected from the group consisting of propylene, n-butene, n-hexane, and n-octene.
 5. The lightweight knit fabric of claim 3, wherein the one or more γ-olefin comonomers is present in an amount of 10 to 30 wt %, based on total yarn weight.
 6. The lightweight knit fabric of claim 2, wherein the linear low density polyolefin has a weight average molecular weight of 10,000 or more.
 7. The lightweight knit fabric of claim 1, wherein the one or more yams has no surface hydroxyl groups.
 8. The lightweight knit fabric of claim 1, wherein the knit fabric is made using a linear stitch or a jersey stitch.
 9. The lightweight knit fabric of claim 1, wherein the fabric has a fabric weight of 10 ounces per square yard (OPSY).
 10. The lightweight knit fabric of claim 1, wherein the fabric comprises up to 4 wt % of an elastomeric yarn.
 11. The lightweight knit fabric of claim 6, wherein the linear low density polyolefin is linear low density polyethylene, optionally containing up to 30 wt % of one or more α-olefin comonomers.
 12. An article prepared from the lightweight knit fabric of claim
 1. 13. The article of claim 12, wherein the article is a garment.
 14. The article of claim 13, wherein the garment is a member selected from the group consisting of shirts, undergarments, socks, leggings, and tights.
 15. The article of claim 13, wherein the garment is a shirt.
 16. The article of claim 14, wherein the shirt is a short-sleeved shirt.
 17. The article of claim 14, wherein the shirt is a long-sleeved shirt.
 18. The article of claim 12, wherein the article is a member selected from bed sheets, pillowcases, and bandages. 